Humidity response of cuticular conductance of beech (Fagus sylvatica L.) leaf discs maintained at high relative water content

Cuticular conductance of adaxial (astomatous) and abaxial (stomatous)surfaces ofFagus sylvatica L. leaves was measured under varyingvapour pressure deficits (D). Conductance was determined fromgravimetric measurements of water flux made using a leaf discenvelope specially designed to maintain leaf relative watercontent and minimize reduction in cuticular hydration. The adaxialsurface provided a determination of ‘true’ cuticularconductance (g_c) and transpiration (E_c). The abaxial surfacewas used to estimate minimum leaf surface conductance (g^MIN_sur)and transpiration (E^MIN_sur). In experiment I, leaf discs wereplaced under one of a range of water vapour pressure deficits(0.4-2.0 kPa). Both g_c and g^MIN_sur decreased approximately 2-foldwith an increase in D between 0.4-2.0 kPa. The decrease in g_cwas linear, but g^MIN_sur declined more steeply at D between 0.4-0.95kPa than at D between 0.95-2.0 kPa. In experiment II, leaf discswere exposed to a stepwise change in D. After a period of acclimationto D of 0.95 kPa, responses of g_c and g^MIN_sur to an increaseor decrease in D were recorded. The response time of g_c to increasingor decreasing D were similar (<60 min). By contrast, g^MIN_surresponded more slowly to increasing than to decreasing D. Thesesignificant responses of g_c and g^MIN_sur to increasing and decreasingD are discussed in relation to hydration state of the cuticleand current knowledge of cuticle structure. Key words: Cuticle, cuticular conductance, cuticular membrane, Fagus sylvatica, humidity, vapour pressure deficit     

AgCl precipitates in isolated cuticular membranes reduce rates of cuticular transpiration

Counter diffusion of chloride, applied as NaCl at the inner side of isolated cuticles, and silver, applied as AgNO₃ at the outer side, lead to the formation of insoluble AgCl precipitates in isolated cuticles. AgCl precipitates could be visualized by light and scanning electron microscopy. The presence of AgCl precipitates in isolated cuticles was verified by energy dispersive X-ray analysis. It is argued that insoluble AgCl precipitates formed in polar pores of cuticles and as a consequence, cuticular transpiration of 13 out of 15 investigated species was significantly reduced up to three-fold. Water as a small and uncharged but polar molecule penetrates cuticles via two parallel paths: a lipophilic path, formed by lipophilic cutin and wax domains, and a aqueous pathe, formed by polar pores. Thus, permeances P (m s⁻¹) of water, which is composed of the two quantities P _Lipid and P _Pore, decreased, since water transport across polar pores was affected by AgCl precipitates. Cuticles with initially high rates of cuticular transpiration were generally more sensitive towards AgCl precipitates compared to cuticles with initially low rates of transpiration. Results presented here, significantly improves the current model of the structure of the cuticular transpiration barrier, since the pronounced heterogeneity of the cuticular transport barrier, composed of lipophilic as well as polar paths of diffusion, has to be taken into account in future.     

Cuticular Membrane Fine Structure of Nicotiana tabacum L. Leaves

The cuticular membrane (CM) ofNicotiana tabacumL., includingthe cellin wall (CW), was examined to gain more informationabout the nature and chemical constitution of its fine structurefor possible inclusion in a model system, as recent literaturequestions its function as a major water permeability barrier.Different preparation techniques were used and the results evaluatedto select a method for future studies on tobacco leaf cuticles.Fixation with OsO₄included in the primary fixative, either asa vapour or in combination with other agents, followed by OsO₄aspost-fixative, gave good contrast of the CM. The lamellar structureof the tobacco cuticle proper (CP) was revealed by contrastingwith uranyl acetate and lead citrate. The fine lamellar structureof the CP was very clearly contrasted when KMnO₄was includedin the primary fixative. This was interpreted as indicatingthe tobacco CP to be polar. The reticulate fibrillar patternof the tobacco cuticular layer (CL) containing polysaccharideswas well contrasted when either OsO₄or paraformaldehyde wereincluded in the primary fixative. Cold fixation with glutaraldehydeand dimethyl sulphoxide and post-fixation with OsO₄revealedelectron-opaque material in the outer cutinized, irregularlyoutlined, region of the CW. These ultrahistochemical reactionsare discussed in relation to the known chemical compositionand possible water permeability of the CM. Cuticular fine structure; cuticular transpiration; Nicotiana tabacumL.     

Persistent Effects of Short-term, High Exposure to Chlorine Gas on Physiology and Growth of Pinus ponderosa andPseudotsuga menziesii

Following a single acute exposure to chlorine gas, persistenteffects on epicuticular waxes, cuticular transpiration, treegrowth and mortality were studied in foliage of Pinus ponderosaand Pseudotsuga menziesii for three growing seasons. Chlorinegas exposure caused foliar injury to both exposed foliage andfoliage that flushed after exposure (P < 0.05). The tendencyto form films of water rather than droplets was greater in directlyexposed foliage (P < 0.001). Rates of cuticular transpirationwere higher for directly and indirectly exposed foliage of Pinusponderosa up to 1 year after exposure and up to 6 months afterexposure for directly exposed Pseudotsuga menziesii(P < 0.001),after which P. menziesii needles defoliated. Total water content(TWC) and relative water content were significantly correlatedwith foliar injury (P < 0.05). TWC was lower for directlyexposed foliage up to 1 year after exposure (P < 0.001).There was no persistent negative effect on F_v/F_m ratios after1 year. Exposure to chlorine gas did not affect needle lengthor annual shoot increment growth, but exposure was correlatedwith increased bud production. Needle longevity of foliage thatflushed 2 months after exposure was reduced significantly (P< 0.001). Annual stem increment growth for both species decreasedover at least three growing seasons following chlorine gas exposure(P < 0.001), and depended on distance from the spill site.Cone production was lower for exposed Pinus ponderosa treescompared to controls (P < 0.05), and tree mortality was higherwithin approx. 50 m of the release site forPseudotsuga menziesii. Growth responses for both conifers agreed well with predictedpatterns of carbon allocation after defoliation caused by chlorinegas exposure. Copyright 2001 Annals of Botany Company Pinus ponderosa, Pseudotsuga menziesii, conifers, chlorine gas, leaf wettability, cuticular transpiration, water relations, growth, mortality     

Limitation of stomatal conductance by hydraulic traits: sensing or preventing xylem cavitation?

We tested the hypothesis that hydraulic conductance per unit leaf surface area of plant shoots (K_SL) determines the maximum diurnal stomatal conductance (g_L) that can be reached by plants growing in the field. A second hypothesis was tested that some xylem cavitation cannot be avoided by transpiring plants and might act as a signal for regulating g_L. Eleven woody species were studied, differing from each other with respect to taxonomy, wood anatomy and leaf habit. Maximum diurnal g_L, transpiration rate (E_L), pre-dawn and minimum diurnal leaf water potential (O_pd and O_min, respectively) were measured in the field. The critical O level at which stem cavitation was triggered (O_cav) was measured on detached branches, using the acoustic method. A high-pressure flow meter was used to measure maximum K_SL of 1-year-old shoots. Both g_L and E_L were positively related to K_SL. The whole-plant hydraulic conductance per unit leaf area (K_WL) of all the species studied, calculated as the ratio of E_L to (O (=O_pd-O_min) was closely related to K_SL. In every case, O_min (ranging between -0.85 and -1.35 MPa in the different species) dropped to the O_cav range or was <O_cav (ranging between -0.71 and -1.23 MPa), thus suggesting that some cavitation-induced embolism could not be avoided. The possibility is discussed that some cavitation-induced reduction in K_SL is the signal for stomatal closure preventing runaway embolism. The lack of correlation of g_L to O_cav is discussed in terms of the inconsistency of O_cav as an indicator of the vulnerability of plants to cavitation. No differences in hydraulic traits were observed between evergreen and deciduous species.     

A leaf disc method for measuring cuticular conductance

This paper describes a new method for the measurement of cuticularconductance (g_o;) using a leaf disc sealed in a specially-designedenvelope. Conductances for astomatous (adaxial) and stomatous(abaxial) surfaces of beech {Fagus sylvatica L.) were determinedfrom measurements of water flux. Leaf discs were punched outfrom attached leaves and placed inside individual envelopesthat provided a water supply. Water flux from an exposed epidermalsurface of the leaf discs was measured gravimetrically. Allmeasurements were made under darkness. Conductance of the adaxialsurface was referred to as g_c, whereas conductance of the abaxialsurface was considered as a minimum leaf surface conductance()- The main advantage of this method is that it enables measurement of g_c and from leaf samples with intact cuticles and a highrelative water content [RWC) for periods of up to 12 d. Conductancesof leaf discs in envelopes were compared with those of wholeleaves and leaf discs without envelopes. Data demonstratinga strong positive relationship between conductance and RWC ispresented. Key words: Cuticular conductance, leaf disc, relative water content     

Vapour Pressure Deficit Response of Cuticular Conductance in Intact Leaves of Fagus sylvatica L.

The cuticular conductance (g_c) of the astomatous adaxial surfaceof Fagus sylvatica L. leaves was determined under varying vapourpressure deficits at a constant temperature of 20 °C. Cuticularconductance was determined from the weight loss of detachedleaves after both the stomatous abaxial surface and the cutend of the petiole had been sealed using low melting-point paraffinwax. Cuticular conductance was found to decrease as the watervapour pressure was increased in steps. No response was observedwhen vapour pressure deficit was decreased from an initiallyhigh value. It is concluded that these results are consistentwith the hypothesis that cuticular conductance is influencedby the water content of the cuticle and that the apparent hysteresisis likely to be a result of the long time-constant for the processof cuticle rehydration in intact leaves. Key words: Cuticle, cuticular conductance, Fagus sylvatica L., Fagaceae, vapour pressure deficit, VPD     

Photosynthesis and Transpiration in Rice as Influenced by Soil Moisture and Air Humidity

The paper describes the effect of soil moisture content andair humidity on CO₂ exchange (P_N), CO₂ diffusion resistance(Cr) and transpiration (E) in four varieties of japonica rice(Oryza sativa L.). A decrease in soil moisture content reducedthe rate of photosynthesis to a varying degree in the varieties.Reduction in photosynthesis was attributed to increase in Cr.The effect of low soil moisture on photosynthesis and CO₂ diffusionwas further intensified by decrease in air humidity. By maintaininga high humidity in the air around the leaves however, the effectof soil moisture deficiency was reduced considerably, exceptin Rikuto Norin 21 which was very sensitive to soil-moisturedeficiency alone. Dryness of the air enhanced the transpirationrate, although the increase was relatively less in the plantsfacing a simultaneous water crisis at the root surface. In plantsgrowing under flooded conditions, a decrease in air humiditycaused a slight depression in P_N despite the simultaneous decreasein Cr. Oryza sativa L., rice, photosynthesis, transpiration, diffusion resistance, soil moisture, air humidity     

Comparative Leaf Surface Morphology and the Glossy Characteristic of Sorghum, Maize, and Pearl Millet

Leaf surfaces of seven genotypes of Sorghum bicolor, two ofmaize, Zea mays, and two pearl millet, Pennisetum americanum,were examined by scanning electron microscopy for possible morphologicaldifferences. Leaves 1, 3, 5 and 7 were photographed and printswere used to estimate waxiness, hairiness or pubescence andstomatal density. Glossiness was determined by spraying water,which adhered to the glossy leaves. Cuticular transpirationof detached third and fifth leaves was estimated from the rateof water loss after abscisic acid induced stomatal closure.Sorghum lines SC283, CSM63, CSM90, and pearl millets Souna andTiotioni (all from Mali), were non-glossy, well covered withwax, and exhibited variable hairiness. Older leaves of sorghumvarieties Martin and Redlan were glossy and, like older leavesof the other glossy lines SC1096 and SC90, had little or nowax deposits on their cuticles. The two maize cultivars, NB611and N7A, were non-glossy with dense wax covering; no trichomeswere observed until the 5 to 7 leaf stage. Thus, the glossycharacter was correlated with the reduction or absence of waxdeposits on the leaf surfaces, while hairiness might occur ineither glossy or non-glossy genotypes. Unlike sorghum and maize,in which all leaves after the fifth or seventh were glossy,pearl millet showed no glossiness through the ninth leaf. Measurementsshowed that cuticular transpiration of glossy leaves was oftenmore than double that of non-glossy leaves. Comparisons amongsorghums showed that non-glossy lines had higher stomatal densitiesthan glossy lines. Epicuticular wax, trichome, glossy mutant, stomata, cuticular transpiration, Sorghum bicolor, (L.) Moench, Zea mays L., Pennisetum americanum, (L.) Leeke     

Production of Oikopleura longicauda (Tunicata: Appendicularia) in Toyama Bay, southern Japan Sea

Oikopleura longicauda occurred throughout the year in ToyamaBay, southern Japan Sea, and analysis of its size compositionand maturity revealed that reproduction was continuous overtheyear. Somatic growth production (P_g) varied with season from0.03 to 103 mg carbon (C) m^–2day^–1 (annual P_g 4.5g C m^–2), and house production (P_e) from 0.11 to 266 mgC m^–2 day^–1 (annualP_e 11.3 g C m^–2). The annualP_g/B ratio was 176. Compared with production data of some predominantzooplankton species in Toyama Bay, it is suggested that despitetheir smaller biomass, appendicularians are an important secondaryproducer.     

Stomatal Responses to Sulphur Dioxide and Vapour Pressure Deficit

Stomatal conductances (g_s) of plants of Vicia faba, Raphanussativus, Phaseolus vulgaris, Heilanthus annuus, and Nicotianatabacum were measured in chambers containing either clean airor air containing between 18 and 1000 parts 10^–9 SO₂ atwater vapour pressure deficits (vpd) ranging from 1·0to 1·8 kPa. When vpd was low (<1·3 kPa at 22 °C) and stomatawere open, exposure to SO₂ induced rapid and irreversible increasesin g_s in V. faba. This response persisted throughout the exposure(3 d). The increase in g_s, 20–30% compared with cleanair, was independent of SO₂ concentration up to 350 parts 10^–9Stomatal conductances of polluted plants at night were greaterthan controls. When stomata were closed before exposure to SO₂,there was no effect on g_s. When vpd was varied, g_s of unpolluted plants of P. vulgarisshowed no response, but that of R. sativus increased slightlywith increasing vpd. In both species exposure to SO₂ causedan increase in g_s at all vpd values. g_s of unpolluted plantsof V. faba, H. annuus, and N. tabacum decreased with increasingvpd. At low vpd values exposure to SO₂ in these species causedan increase in g_s, but, above a certain value of vpd, dependingon species, g_s decreased with exposure to SO₂. It is postulated that SO₂, once in the substomatal cavity, entersthe stomatal complex via adjacent epidermal cells and at lowconcentrations leads to a reduction in turgor in these cellsand consequently to stomatal opening. In vpd-sensitive species,increased transpiration from guard cells or epidermal cellsadjacent to the stomata induced by SO₂ may lead to stomatalclosure at large vpd levels. Stomatal sensitivity to vpd insuch cases may be enhanced because adjacent epidermal cell turgoris lowered by SO₂. At high SO₂ concentrations direct disruptionof guard cell structure may lead to a loss of turgor and stomatalclosure.     

Cuticular permeability of the three tree species Prunus Iaurocerasus L., Ginkgo biloba L. and Juglans regia L.: comparative investigation of the transport properties of intact leaves, isolated cuticles and reconstituted cuticular waxes

Cuticular transport properties of intact leaves, isolated cuticularmembranes and reconstituted cuticular waxes of the three treespecies Prunus laurocerasus L., Ginkgo biloba L. and Juglansregia L. were measured using six different ¹⁴C-labelled compounds,benzoic acid, salicylic acid, 2,4-dichlorophenoxy acid, metribuzin,4-nitrophenol, and atrazine. For the same compound and the samespecies, the permeance of the intact leaf and the isolated cuticlewas equal. This provides strong evidence demonstrating thattransport properties of cuticles are not altered during isolation.Additionally, diffusion coefficients of the ¹⁴C-labelled compoundsin isolated and subsequently reconstituted cuticular wax ofthe three tree species were measured. Permeances of intact leavesand isolated cuticles could be predicted from diffusion coefficients,wax/water partition coefficients and the thickness of the transport-limitingwax layer with a mean deviation of about 1.7. This providesevidence that transport properties of recrystallized cuticularwaxes do indeed reflect barrier properties of isolated cuticularmembranes and intact leaves with in situ waxes. Thus, it canbe concluded that the investigation of cuticular permeabilityusing the three independent experimental systems of differentcomplexity give comparable results. Finally, it was observedthat permeances and diffusion coefficients measured with P.laurocerasus were always significantly lower than those measuredwith G. biloba and J. regia. This is interpreted as an ecologicaladaptation of the respective species. The evergreen speciesP. laurocerasus must be more adapted to environmental stresssuch as drought and frost injury compared to the two deciduousspecies G. biloba and J. regia. Key words: Cuticular permeability, diffusion coefficient, leaf surface, permeance, plant cuticle, transport     

A Method for Separating Cuticular and Stomatal Components of Gas Exchange by Amphistomatous Leaves: II. EXPERIMENTAL SOLUTION

The apparent cuticular component of transpiration of stomatabearing leaf epidermis was estimated by restricting stomataldiffusion by mass flow of air in the opposite direction. Thiswas achieved by applying an air pressure gradient across theamphistomatous leaf. Some assumptions of the previously suggestedmethod (antrcek and Slav?k, 1990) were experimentally verifiedusing maize leaves. The technique makes possible a quantitativeestimation of cuticular water loss including that of the externalperistomatal (i.e. vapour not passing through the pores) andthe respective conductance when the stomata are partially open. In addition to the fact that the cuticular portion of the totalleaf vapour loss (i.e. relative cuticular transpiration) dependson stomatal opening, even the absolute value of apparent cuticulartranspiration was (1) increased by lower vapour pressure deficitand (2) decreased with closing stomata. These changes, inducedby variations in a vapour pressure deficit of 2.45?0.35 kPa,ranged between 0.66?0.14µg cm ^–2 s^–1. Theabsolute value of apparent cuticular transpiration changed onaverage by a factor of 2.3 due to stomata opening or closingwhich was induced by turning the light on or by exogenous ABAapplication. Possible interference by residual vapour diffusingthrough the stomatal pore was evaluated by the model application.An attempt was also made to assess the cuticular component ofCO₂-uptake rate. Experimental results are discussed in contextwith the feedforward response of stomata to air humidity. Key words: Cuticular transpiration, cuticular CO₂-uptake, feedforward response, maize     

Water relations and hydraulic architecture of woody hemiepiphytes

Several parameters related to the water relations of eight woodyhemiepiphytes with different photosynthetic pathways were studiedin situ and in the laboratory on Barro Colorado Island, Panama.As a group, woody hemiepiphytes tended to have less conductivestems per unit leaf area (lower k_L) and invested less wood cross-sectionper unit leaf area compared to free-standing trees, while theirspecific conductivity (K_s) was significantly higher. Among hemiepiphytes,there were significant differences between C₃ and CAM (CrassulaceanAcid Metabolism) species in respect to leaf characteristics,transpiration rates, diel patterns of water flow through aerialroots, and in hydraulic architecture parameters. Average transpirationrates of the two Clusia species (C₃-CAM) were lower by aboutan order of magnitude compared to the C₃ species. In all C₃species, sap flow through aerial roots (F) closely followedtranspiration (E), whereas E and F were decoupled in time inthe C₃-CAM species Clusia uvitana: considerable long-distancewater flow occurred at night. The hydraulic efficiency of theother C₃-CAM species, C. minor was the lowest of the five speciesinvestigated. Key words: Hemiepiphytes, water relations, hydraulic architecture, aerial roots, CAM     

Root Hydraulic Conductivity of Two Cactus Species in Relation to Root Age, Temperature, and Soil Water Status

The effects of root age, temperature, and soil water statuson root hydraulic conductivity (L_P) were investigated for twocactus species, Ferocactus acanthodes and Opuntia ficus-indica.The volumetric flux density of water was measured for excisedroot segments, either using negative hydrostatic pressures appliedto the proximal end or using reverse flow of water from theroot to the soil. For both species, L_P at 20 ?C increased withroot age, average values reaching a maximum of 3.9 ? 10^–7m s^–1 MPa^–1 for F. acanthodes and 5.2 ? 10^–7m s^–1 MPa^–1 for O.ficus-indica at 11 to 17 weeksof age; L_P subsequently declined with increasing root age forboth species. L_P was maximal at a temperature of about 10 ?Cfor the youngest roots (1–3 weeks), this optimum shiftingto 40 ?C for 8-week-old roots of both species. For older roots(up to 1.5-years-old), L_P increased with temperature from 0?C to 50 ?C, with a Q₁₀ of 1.3 between 20 ?C and 30 ?C. At asoil water potential (_soil) of –0.016 MPa, root L_P wasindependent of the direction of water flow for both species.Depending on root age, L_P declined 45- to 500-fold for F. acanthodesand 90- to 800-fold for O.ficus-indica as _soil was reduced from–0.016 to –1.06 MPa, consistent with a rectifier-likebehaviour with respect to water movement between soil and roots.Incorporation of such responses into water uptake models shouldlead to a better understanding of root function. Key words: Ferocactus acanthodes, Opuntia ficus-indica, water potential, tension, reverse flow     

The Effect of Reduced Hydraulic Conductance on Stomatal Conductance and Xylem Cavitation

The vulnerability of xylem conduits to cavitation theoreticallydetermines the maximum flow rate of water through plants, andhence maximum transpiration (E), stomatal conductance (g_s),and leaf area (A₁. Field-grown Betula occidentalis with a favourablewater supply exhibit midday xylem pressures (     

Root Water Uptake, Leaf Water Storage and Gas Exchange of a Desert Succulent: Implications for Root System Redundancy

A technique used for hydroponics was adapted to measure instantaneousroot water uptake from the soil for a leaf succulent CAM species,Agave deserti. Comparisons were made to previously modelledwater fluxes for A. deserti and to Encelia farinosa, a non-succulentC₃species. Net CO₂uptake and transpiration forA. deserti underwell-watered conditions occurred primarily at night whereasroot water uptake was relatively constant over 24 h. Leaf thicknessdecreased when transpiration commenced and then increased whenrecharge from the stem and soil occurred, consistent with previousmodels. A drought of 90 d eliminated net CO₂uptake and transpirationand reduced the water content of leaves by 62%. Rewetting theentire root system for 7 d led to a full recovery of leaf waterstorage but only 56% of maximal net CO₂uptake. Root water uptakewas maximal immediately after rewetting, which replenished rootwater content, and decreased to a steady rate by 14 d. Whenonly the distal 50% of the root system was rewetted, the timefor net CO₂uptake and leaf water storage to recover increased,but by 30 d gas exchange and leaf water storage were similarto 100% rewetting. Rewetting 10 or 20% of the root system resultedin much less water uptake; these plants did not recover leafwater storage or gas exchange by 30 d after rewetting. A redundancyin the root system of A. deserti apparently exists for dailywater uptake requirements under wet conditions but the entireroot system is required for rapid recovery from drought.Copyright1999 Annals of Botany Company Agave deserti Engelm., desert, drought, gas exchange, rewetting, roots, succulent, water uptake.     

Effect of temperature on cuticular transpiration of isolated cuticular membranes and leaf discs

Cuticular transpiration was measured in the temperature range between 10 degrees C and 55 degrees C using tritiated water and five species (Vinca major L., Prunus laurocerasus L., Forsythia intermedia L., Citrus aurantium L., and Hedera helix L.). Cuticular water permeabilities measured with isolated cuticular membranes were not different from cuticular water permeabilities measured with leaf discs. Depending on the species cuticular water permeabilities increased by factors between 12 (V. major) to 264 (H. helix) when temperature was increased from 10 degrees C to 55 degrees C. Arrhenius plots (lnP versus 1/T) of all investigated species were characterized by phase transitions occurring in the temperature range of 30-39 degrees C. Activation energies for water permeability across plant cuticles below and above the midpoint of phase transition were calculated from Arrhenius plots. Depending on the species they varied between 26 (F. intermedia) to 61 kJ mol(-1) (H. helix) below the phase transition and from 67 (V. major) to 122 kJ mol(-1) (F. intermedia) above the phase transition. Since the occurrence of phase transitions always lead to significantly increased rates of cuticular transpiration it is argued that temperatures higher than 35 degrees C caused structural defects to the transport-limiting barrier of the plant cuticles of all species investigated.     

Leaf Properties Related to the Photosynthetic Response to Drought in Upland and Lowland Rice Varieties

Four upland and two lowland varieties were grown on floodedand dry soil in pots in a glasshouse. Photosynthetic rate (P),transpiration rate (T), and water content (W) of the secondexpanded leaf from the top of the main stem were measured undercontrolled aeration and illumination in a leaf chamber in thelaboratory, together with leaf area (La), dry matter content(DM), nitrogen content (N), stomatal frequency (Sf), and totalvessel cross-sectional area at the base of the leaf blade (Va).P/La was positively related to T/La and Sf/La among six varietieswhen they were grown on flooded soil. IR 8, a semidwarf indicalowland variety, showed the highest P/La with the highest Sf/Laand T/La. When grown on dry soil P/La was positively correlatedwith W/DM, the latter being negatively related to T/Va. Twoupland varieties, African Moroberekan and Brazilian IAC 1246,showed the highest P/La on dry soil, keeping a higher W/DM witha lower T/La and a lower T/Va. Daytime leaf diffusive conductance(l/r_L) and leaf water potential (_L) measured on the same orthe same stage leaf in the glasshouse were positively correlatedwith the W/DM measured in the laboratory among varieties grownon dry soil. Simultaneous observation of P, T and W in the laboratoryindicated nonstomatal reduction in P/La due to leaf water deficitin sensitive varieties, although these varieties also showeda markedly lower daytime l/r_L in the glasshouse as comparedwith resistant varieties. Oryza sativa L., rice, drought resistance, photosynthesis, transpiration, water deficit, stomatal frequency, vessel size     

Reproductive Allometry in Soybean, Maize and Sunflower

We compared the relationship between grain yield per plant (Y_P)and shoot biomass per plant (S_P) in three annual crops withcontrasting reproductive strategies: sunflower, a determinatespecies with a single inflorescence; maize, a determinate specieswith a limited capacity to adjust the number of ears in responseto resource availability; and indeterminate soybean, a specieswith a large capacity to adjust the number of inflorescences.Our working hypotheses were: H₁—the relationship betweenY_PandS_P is linear; H₂—the intercept of the model is zero,i.e. there is not a threshold plant mass for reproduction. Awide range of Y_Pand S_Pwas generated by manipulation of plantdensity;S_Pvaried between 0.3 and 196 g per plant in soybean,between 6 and 873 g per plant in sunflower and between 23 and697 g per plant in maize. Within these broad ranges of plantsize, both hypotheses were rejected in five out of six experiments,i.e. the relationship between Y_Pand S_Pdeparted from linearityand there was a threshold for S_Pbelow which no grain set occurred.TheS_P threshold for grain set varied widely among species; itwas close to 2 g per plant for soybean, 27 g per plant for sunflowerand 43–71 g per plant for maize. Because of this sizethreshold and non-linearity, harvest index (HI = Y_PS_P^-1) wasstable for mid-size plants, diminished slightly for large plants,and diminished sharply for smaller plants in all three crops.Harvest index stability was highest in soybean, intermediatein sunflower and lowest in maize. Differential stability ofreproductive partitioning partially derived from contrastingpatterns of meristem allocation. Copyright 2000 Annals of BotanyCompany Helianthus annuus L., Zea mays L., Glycine max(L.) Merrill, grain yield, harvest index, plant density, reproductive allocation, meristem allocation, plasticity